AbbreviationsAOX Organically bound halogen(s)bp Base pair(s)BSA Bovine serum albumindbRDA Distance-based redundancy analysisFH Fermentation organic soil horizonHEX 6-Carboxy-4,7,2′,4′,5′,7′-hexachlorofluoresceinITS Internal transcribed spacerPCR Polymerase chain reactionTRF Terminal restriction fragmentT-RFLP Terminal restriction fragment lengthpolymorphismIntroductionChlorine belongs to the 20 most abundant elements on theEarth's surface. The main source of chloride ions in theforest ecosystem is the oceans, in spite of the fact that morechlorine is contained in the Earth's crust and mantle(Graedel and Keene 1996; Winterton 2000). Chlorinebound to organic matter may originate from varioussources. In forest ecosystems, it is mainly present asorganically bound chlorine or as chloride ion in the soiland in the biomass. It contributes to the degradation of soilorganic matter, which represents the major sink of carbon inthe forest ecosystem. Forest soil organic matter is formedmostly from litter, which is decomposed largely bybasidiomycetes (DeJong and Field 1997). The content ofchloride in the environment depends on the geographicsituation, i.e., on distance from the sea, while organicallybound chlorine is connected with the biogeochemicalcycling (Oberg 1998, 2002, 2003; Johansson et al. 2003).The organically bound halogen (AOX) concentrations inthe soil of a coniferous forest ecosystem in Scandinaviaalways exceeded those of chloride (Oberg 2003).Chlorinated organic compounds are thus not only ofanthropogenic origin (e.g., chlorinated solvents, PVC,PCBs, or insecticides) as though in the past. They arepresent in forest soils, are relatively stable, and, as some ofthem are soluble, they can penetrate into groundwater. Theymay thus represent a potential menace in regions withdrinking water reservoirs. Many hundredths of chlorinatedorganic compound were found in nature (Winterton 2000;Gribble 2003; Clarke et al. 2009), which are often producedfrom deposited sea salt in the processes mediated byhalogenating enzymes of peroxidase nature and alsoabiotically (Shaw and Hager 1959; Clarke et al. 2009).Forest soil microbiota interact with the natural chlorinecycle. This is reflected in changes in composition of the soilmicrobial community when the soil was incubated at highchloride concentration (Gryndler et al. 2008). Further,